Pinus afforestation in South Brazilian highlands: soil chemical attributes and organic matter composition

Deborah Pinheiro Dick,Henrique Cesar Almeida,Simone Benvenuti Leite,Heike Knicker,Ricardo Simão Diniz Dalmolin

doi:10.1590/s0103-90162011000200007

Deborah Pinheiro Dick, Henrique Cesar Almeida + Show 3 more

Open Access

https://doi.org/10.1590/s0103-90162011000200007

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Abstract

In the last three decades, exotic tree species are being introduced in the natural pastures of the highlands located at the northeastern part of Rio Grande do Sul State (RS), Brazil. This alteration of land use may impart drastic changes in the soil attributes. In this context, this work aimed to evaluate the impact of Pinus taeda afforestation on soil chemical attributes and organic matter (SOM) composition in Leptosols from Campos de Cima da Serra, RS. Soil samples under eight year old (Pi8) and 30 year old (Pi30) Pinus plantations and under native pasture (NP) were studied. Contents of exchangeable cations and of micronutrients and soil pH were determined. The SOM composition was investigated by means of elemental analyses and FTIR spectroscopy. The soil under pasture had a higher content of nutrients and of SOM in comparison to Pinus soils, reflecting the higher input and decomposition rate of the below ground added residue in the grassland environment. The SOM in pasture soils showed a higher content of carbohydrate and of structures derived from microbial metabolism. Besides the depletion of nutrients and of SOM, Pinus afforestation affected the SOM quality: following afforestation, the proportion of chemically recalcitrant structures and of carboxylic groups increased, whereas N-containing groups decreased.

Highlights

The afforestation of a degraded land with exotic trees has been a strategy lately used to improve soil quality, promote C sequestration and simultaneously produce an economic return
The soil samples were highly acidic (4.1 ≤ pH-H2O ≤ 4.6) and no difference between treatments and depths were observed (Table 1). This behaviour is typical for lowly weathered highland soils from Southern Brazil, and is usually associated with the occurrence of a considerable amount of organic acids, which accumulate in the soil due to the slow decomposition and mineralization of the vegetal residues in comparison to soils from warmer and drier climates (Silva et al, 2008)
As already observed by Wiesmeier et al (2009), the greatest values for C content were found in the samples under native pasture and a sharp decrease of this attribute with soil depth was observed (Table 1)

Summary

Introduction

The afforestation of a degraded land with exotic trees has been a strategy lately used to improve soil quality, promote C sequestration and simultaneously produce an economic return. The soils are shallow (mostly Leptosols, Umbrisols and Cambisols), strongly acid (pH around 4.2) and alic, with high contents of SOM in the surface layer (higher than 4%) (Silva et al, 2008). Their SOM presents a low level of humification, estimated by its high proportion of C-O alkyl groups (51 to 59%) (Dick et al, 2008), in comparison to the values usually observed for Oxisols from the same latitude (Dick et al, 2005). Soil disturbance or alteration of the C dynamic balance due to a change of vegetation may cause a reduction in SOM and soil quality as already observed by the introduction of agriculture on former pastures in the subtropics (Dieckow et al, 2005)

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